ABSTRACTS OF MEMOIRS. 245 



On a red background and on a green background in white liglit 

 Hippohjtc become orange and green respectively. 



The production of sympathetic colouring in the shallower coastal 

 waters is explained as a background efiect. The production of crimson 

 Hippolytc (and possibly of reddish varieties of other marine animals) 

 in deeper water is explained as due to diffused green light. 



There is no evidence that the pigments of the algal food are the 

 sources of the pigments in Hippohjtc varians. 



F. W. G. 



The Reproduction and Early Development of Laminaria digitata 

 and Laminaria saocharina. By G. H. Drew. Ann. But., Vol. 

 XXIV, No. xciii., January, 1910, p. 177. 



Laminaria digitata and L. saccharina are among the commonest sea- 

 weeds found on the coasts of the British Isles ; they form the greater 

 part of the " kelp " which is collected in some places for commercial 

 purposes. 



In the autumn and winter dark brown patches appear near the 

 extremities of the broad flattened fronds, and in these the repro- 

 ductive cells are formed. When ripe, small pieces of these reproduc- 

 tive areas were placed in a special culture solution (Allen and Nelson's 

 modification of Miquel's solution), and it was foimd that an immense 

 number of minute, free swimming cells were liberated. These cells 

 each have two flagella, by means of which they are enabled to 

 swim actively, and they show a tendency to move towards any source 

 of light. Though all are exactly similar in appearance, yet these cells 

 must be regarded as the sexual cells of the plant. After a time they 

 fuse in pairs, lose their flagella, and settle to the bottom of the 

 culture fluid. A series of changes then takes place resulting in the 

 formation of a chain of cells possessing colouring matter, and appar- 

 ently capable of absorbing nutrition, and of growth. This chain of 

 cells can be considered as a separate plant, which though of an 

 extremely rudimentary type, yet has an independent existence. 

 Eventually any cell of the chain may give rise directly to a young 

 Laminaria plant. 



Thus in the life cycle of Laminaria, an alternation of generations 



occurs : the Laminaria plant represents the sexual phase, and the 



microscopic chain of cells above mentioned represents the asexual 



phase. 



G.H.D. 



